A clock generator circuit produces one or more clock signals (also referred to as “clocks”) for use in synchronizing the operation of digital blocks. A clock signal can be, for example, a symmetrical square wave. A conventional clock generator includes a resonant circuit and an amplifier. The resonant circuit may be a quartz piezo-electric oscillator, a tank circuit or an Resistor-Capacitor (RC) circuit. The amplifier inverts the signal from the oscillator and feeds a portion back into the oscillator to maintain oscillation. The clock generator may include a frequency divider or clock multiplier, which can be programmed to allow a variety of output frequencies to be selected without modifying hardware.
In low power microcontrollers that use conventional clock generator circuits, a clock signal for a digital block may run continuously even if the clock signal is not needed by the digital block, resulting in wasted power.